Propellant composition containing high energy metal in the form of multi-di-mensional crosses



June 18, 1968 J, NIX L 3,389,025

PROPELLANT COMPOSITION CONTAINING HIGH ENERGY METAL IN THE FORM OF MULTI-DIMENsIoNAL CROSSES Filed March 22, 1967 (PRIOR ART) Joseph E. Nix

Winford 6. Brock,

INVENTORS.

United States Patent Office 3,389,025 Patented June 18, 1968 ABSTRACT OF THE DISCLOSURE A novel shape for metal staples used as a, burning rate modifier for solid propellant grains. The shape is that of a multi-dimensional cross.

Background of the invention This invention relates to an improved staple design and particularly to one used as a burning rate modifier for solid propellant grains.

Metal staples, that is, thin fragments of metal wire, strip or filament are employed in solid propellant grains to obtain improved burning characteristics. Incorporation of metal staples throughout the grain provides substantially accelerated burning rates by increasing conduction of heat from the burning surface to the interior of the grain. The staples also serve as a source of high energy fuel in the propellant composition, the metal employed being aluminum, magnesium, zirconium or other metal or alloy which releases a large amount of energy upon combustion. Staple-containing propellant compositions are particularly useful in rapid-accelerating rocket motors that require minimum time from launch to target.

One of the problems presented in the use of metal staples in propellant grains is orientation of the staples in the desired manner. For maximum effectiveness, the staples should be oriented with their longest axis perpendicular to the direction of burning. Orientation parallel to the direction of burning is undesirable in that a minimum of reproducibility is realized.

Control of staple orientation has proven to be a particularly diflicult task for propellant grains prepared by slurry casting. In applicants composition, the uncured propellant composition, while in a pasty gel state, is poured into a mold of the desired con-figuration, normally an elongated cylindrical container having an axially disposed mandrel in its center to produce an internal perforation. The internal perforation provides a burning surface extending throughout the body of the grain, and the amount of burning surface is controlled by varying the design of the perforation. In casting grains of this type, the staples tend to become aligned parallel to the direction of flow of the propellant composition, which is at least partially parallel to the mold and mandrel walls. As a result, the staples are oriented parallel to the burning surface at the internal perforation and outer edge of the grain. Perpendicular, rather than parallel, orientation with respect to the burning surface is particularly desired at these locations. Perpendicular orientation at the internal perforation would provide a high initial burning rate and rapid attainment of maximum thrust. Similarly, perpendicular orientation along the outer wall of the grain would produce rapid burning when the last portions of the propellant grain are being consumed so as to retain a high thrust for the longest possible period.

It is, therefore, the principal object of this invention to provide a metal staple whereby malalignment of the staple is impossible when incorporated in a propellant composition.

Summary of the invention This invention provides an improved staple design such that orientation of the staples parallel to the burning surface is impossible. A random distribution effect is achieved.

Although several designs are possible, the preferred embodiment of this invention employs a multi-dimensioned cross. Specifically, the staple construction consists of a two-dimensional cross in a horizontal plane with another length of the material being used in a plane perpendicular to the aforementioned cross, and passing through the intersection of the cross arms. All arms of the resulting multi-dimensional cross are preferably equal in length.

Brief description of the drawing Other objects and advantages of this invention will be apparent from the description that follows, from the appended claims and from the drawing, in which:

FIGURE 1 is a cross-sectional view of a motor casing employing a propellant grain containing a prior art staple design;-

FIGURE 2 is a cross-sectional view of a motor casing employing a propellant grain containing a staple design of this invention; and

FIGURE 3 is a perspective view of a staple of this invention.

Description of the preferred embodiment Referring now to FIGURES l and 2, there is shown generally cylindrical motor cases 1 which serve as casting molds. A cylindrical mandrel 2 is disposed axially in each of motor cases 1 to form an internal perforation extending the full length of the grain. To illustrate the principleinvolved, a comparison between conventional staples 3 and the improved staple design 4 of this invention in the motor cases is depicted in FIGURES 1 and 2. It can be seen in the case of conventional staples 3 that a wall effect exists at the walls of motor case 1 and mandrel 2. Conversely, with the improved staple design 4 of this invention (FIGURE 3), this effect cannot occur because some portion of the staple will always be aligned perpendicular to the direction of burning. The random orientation which occurs is enough to minimize the wall effect.

Normally, propellant staples consist of circular fragments of wire about ,5 to inch long and 5 to 20 microns in diameter or metal strips of the same length, 0.0045 to 0.04 inch wide and 0.0008 to 0.008 inch thick. The staple design of this invention (FIGURE 3) preferably has arms about to inch long and 5 to 20 microns in diameter (or width and thickness).

This invention is applicable to staple-containing propellant compositions which exhibit physical properties in the uncured state for fabrication by casting (preferably low viscosity), and the chemical composition of the propellant composition is not critical. In general, this invention is useful for composite-type propellant compositions comprising a liquid polymeric binder such as polysulfides, polyurethanes, polydienes, polydiene-acrylic acid copolymers and the like, an inorganic oxidizing agent such as ammonium perchlorate or other nitrate or chlorate salt and other additives such as curing agents and burning rate catalysts along with the metal staples. Propellant compositions of this type normally contain a relatively large amount such as 20 to 50 weight percent of the solid-phase oxidizer so that the uncured composition is a relatively low viscosity slurry formulation. Metal staples typically comprise about 3 to 7 weight percent of the composition. Other types of staple-containing propellants such as double-base propellants employing nitrocellulose assapzs as the propellant binder and a nitrate ester plasticizer may also be fabricated according to this invention.

The propellant composition is poured to the desired level in the motor case mold and the resulting propellant grain is cured to impart strength and rigidity therein. Previously known curing methods, which normally involve the application of mild heat for an extended period, may be employed.

It is thus seen that improved solid propellant compositions can be made according to this invention. The use of the herein described cross design keeps staples from being aligned with respect to the burning plane of the propellant; that is, it gives a random distribution effect. This provides for a maximum and more reproducible burning of propellant grains It is to be understood that various changes and modifications may be employed Without departing from the spirit and scope of this invention.

We claim:

1. A composition for solid propellants having incorhaving arms in a first plane, and two other arms located in a plane perpendicular to said first plane and passing through the intersection of the arms of said twodimensional cross.

2. The composition of claim 1 wherein said two-dimensional cross is equilateral.

.3. The composition of claim 1 wherein all of said arms of said multi-dimensional cross are of the same length.

4. The composition of claim 3 wherein said composition is of low viscosity.

5. The composition of claim 4 wherein said composition comprises an oxidizing agent, a liquid polymeric binder and a curing agent.

6. The composition of claim 5 wherein said arms are about one eighth of an inch long.

7. The composition of claim 5 wherein said arms are generally circular in cross section and about ten microns in diameter.

8. The composition of claim 6 wherein said arms are generally circular in cross section and about ten microns lll diameter.

References Cited lTJNlTED STATES PATENTS BENJAMIN R. PADGETT, Primary Examiner. 

